In recent years, two-component urethane coating compositions used as solvent-based paints have been required to be aqueous from the viewpoint of environmental protection. However, polyisocyanates, which are used as curing agents in two-component urethane coating compositions, are poorly dispersible in and highly reactive with water, and their reaction with water produces carbon dioxide. Thus, there have been developed polyisocyanates that have emulsifiability and whose isocyanate groups do not readily react with water even when they are dispersed in water.
For example, Patent Literature 1 discloses a water-dispersible polyisocyanate mixture containing a polyisocyanate compound and a polyether containing an ethylene oxide unit. Patent Literature 2 discloses a polyisocyanate composition that is easily dispersible in water, the polyisocyanate composition being obtained by a reaction between a prepolymer formed from an aliphatic or alicyclic diisocyanate and a nonionic hydrophilic component made up of an average of 3.0 to 4.9 ethylene oxide repeating units. Patent Literature 3 discloses a polyisocyanate composition obtained by a reaction with a nonionic hydrophilic component having at least one hydroxy group and made up of 3 to 50 ethylene oxide repeating units and a long-chain polyol component having a number-average molecular weight of 1000 to 15000.